If the Bank 2 O2 sensor isn't showing any voltage fluctuation, my guess would be the following:
A) There is a malfunction in the heater circuit for that sensor.
B) There is a bad connection on that sensor.
Might want to try cleaning the contacts for that sensor before you replace it.
The cat monitor runs really late in the scheme of things.
Drive cycle page will give you info on when the different monitors run, and what conditions cause them to run. Although Cat Monitor is step 7 here, the condiions for it are generally the last to be satisfied in regular driving from my experience.
I would have expected a CEL from a constant low voltage O2 sensor - sure there isn't a "pending code" or PTC stored (wouldn't throw a CEL)? Once the heater warms the element to its operating temperature, it should begin to switch (albeit slowly for a downstream sensor). Until the element is heated, the voltage won't go above 0.05V or so (true for all the O2 sensors). Heating is supposed to occur within about a minute or so of engine on.
Hope this helps.
